Sustaining the gait locomotion in an adversarial environment requires the robot to react to novel experiences adaptively. In Free Energy Principle (FEP), the behavioral reaction is driven by the discrepancy between observation and prediction. Although, for legged robot gait locomotion, the prediction of gait dynamics is challenging as the consequences non-linearly depend on the activity history, the animal gait is robust, adapting to severe motion disruptions seemingly instantly. In biomimetic robotics, the Central Pattern Generator (CPG) relaxes the general dynamics of body-environment interaction to the stable and repetitive dynamics of gait. Based on these observations, we propose self-learning of the gait dynamics model and FEP framework that infers state estimation and gait control. The proposed method is experimentally evaluated on a real hexapod walking robot with 18 controllable degrees of freedom. The robot learns the gait dynamics model indoors and then deploys it in outdoor navigation under various adversarial scenarios. Results show that the developed interpretable gait controller exhibits complex and real-time adaptive behavior when it encounters unknown situations.

Sustaining the robot's longevity becomes challenging in dynamic deployments characterized by new unknown environments and embodiments outside of the prior knowledge. Hence, the knowledge of robot-environment interactions needs to be continually updated for system adaptation. It can be implemented through self-verification as a continual comparison of predictions with observations using the predictive coding (PC) principle. The principle has been further extended into the active inference control (AIC) in biomimetic robotics to drive the control, state estimation, and model update. However, continually updating one model leads to catastrophic forgetting in the long term. Therefore, we propose an autonomously expanding self-verifying world model (WM) of sensorimotor dynamics utilized in model-based gait control. The model combines PC with the incremental knowledge representation based on the internal model (IM) principle. The proposed method is experimentally validated in virtual and real scenarios, where the hexapod walking robot has to recognize and adapt to leg paralysis and then recognize the recovery. The method generates novel behaviors in real time, improving the performance and outperforming the examined state-of-the-art methods. Furthermore, the robot's decisions and gained knowledge are interpretable and promise further functional scalability.

In the paper, we address wireless communication infrastructure building by relay placement based on approaches utilized in wireless network sensors. The problem is motivated by search and inspection missions with mobile robots, where known sensing ranges may be exploited. We investigate the relay placement, establishing network connectivity to support robust food-based communication routing. The proposed method decomposes the given area into Open space and Corridor space where specific deployment patterns allow for guaranteed k-connectivity, making the resulting network redundant while keeping channel utilization bounded. In particular, a hexagonal tesselation coverage pattern with 3-connectivity is investigated in Open space and a linear 4-connectivity pattern in Corridor space, respectively. The proposed approach is empirically evaluated in a realistic scenario, and based on the reported results, it is found superior compared to the existing stochastic randomized dual sampling schema.

In this paper, we focus on improving planning efficiency for ground vehicles in navigation and exploration tasks where the environment is unknown or partially known, leading to frequent updates of the navigational goal as new sensory information is acquired. Asymptotically optimal motion planners like RRT* or FMT* can be used to plan the sequence of actions the robot can follow to achieve its current goal. Frequent replanning of the whole action sequence becomes computationally demanding when actions are not executed precisely because of limited information about the foreground terrain. The decoupled approach can decrease the computational burden with separated path planning and path following; however, it might lead to suboptimal solutions. Therefore, we propose a novel approach based on generating a reusable reward function that guides a fast sampling-based motion planner. The proposed method provides improved results in navigation scenarios compared to the former approaches, and it led to about 7% faster autonomous exploration than the decoupled approach. The present results support the suitability of the proposed method in navigation tasks with continuously updated navigation goals.

In this paper, we address the sensitivity of the 3D LiDAR-based localization to environmental structural ambiguity. Although existing approaches employ additional sensors, such as cameras and inertial measurement units, to account for such ambiguities, multi-sensor localization is still an open problem. Limitations are from the need to tune fusion parameters to compensate for limited ambiguity detection manually. Therefore, we propose a feature-based localization method that learns the fusion parameters using ground truth and thus supports autonomous mobile robotic systems in new locations. The method combines planar surface LiDAR features with close and far camera features, and its further advantage is an online adjustment of the feature weights based on the measured environment ambiguity. The evaluation has been performed on the existing M2DGR dataset and custom dataset with geometrical ambiguities. The proposed method is competitive to or outperforms the existing LiDAR-based methods F-LOAM and LIO-SAM and the Visual-Inertial localization method VINS-Mono. Based on the reported results, the proposed method is a vital combination of LiDAR-based and visual features.

Mobile robots operating in convoys have a limited view of the terrain to be traversed if it is occluded by the preceding vehicle. Furthermore, the preceding vehicle might change the terrain geometry and eventually significantly alter its traversability by driving over the terrain. When the following vehicles do not consider such changes, they can use spurious terrain appearance and geometry to decide whether to follow in the tracks of the previous vehicle or to avoid them since the preceding vehicle’s tracks can make the terrain untraversable. We propose to predict the terrain changes induced by the robot traversal on the traversed terrain and thus support the decision-making of the following vehicles. The developed model projects the robot wheel footprint along the planned robot path and combines the projection with the terrain appearance and prior terrain elevation. The coupled model is used in a convolutional neural network that predicts the elevation after traversal. The footprint projection component is designed so that learned networks can be transferred to vehicles with different wheel footprints without relearning the model. The proposed model is verified using a dataset captured using a real, one-ton, six-wheel robot traversing rigid roads and vegetated fields.

With the rapid development of advanced sensing, communication, and the industrial Internet of Things, it has become much easier to obtain, transmit, and, store a massive amount of real-world data. However, imperfect data is inevitable in real-world systems, such as the existence of outliers, contaminated, incomplete, inaccurate, and even missing information in the data. This phenomenon is called data imperfection, which usually makes traditional datadriven modeling and automation methods either unfeasible or ending at undesired inaccuracies. This has been a wellknown challenge to data-driven methods when applied to real-world systems, such as process industry, manufacturing, energy networks, and transportation systems.

In this paper, we propose a novel dynamic gait controller for the repetitive behavior of soft robot manipulators performing routine tasks. Compliance with soft robots is advantageous when the robot interacts with living organisms and other fragile objects. However, predicting and controlling repetitive behavior is challenging because of hysteresis and non-linear dynamics governing the interactions. Existing priorfree methods track the dynamic state using recurrent neural networks or rely on known generalized coordinates describing the robot's state. We propose to model the interaction induced by the repetitive behavior as gait dynamics and represent the dynamic state with Central Pattern Generator (CPG) tracking the motion phase and thus reduce the complexity of the robot's forward model. The proposed method bootstraps an ensemble of the forward models exploring multiple dynamic contexts that are expanded as it searches for repetitive motion producing the target repetitive behavior. The proposed approach is experimentally validated on a pneumatically actuated soft robot arm I-Support, where the method infers gaits for different targets.

An in-flight loss of thrust poses a risk to the aircraft, its passengers, and people on the ground. When a loss of thrust happens, the (auto)pilot is forced to perform an emergency landing, possibly toward one of the reachable airports. If none of the airports is reachable, the aircraft is forced to land at another location, which can be risky in urban environments. In this work, we present a generalization of the previous work on planning safe emergency landing in the case of in-flight loss of thrust such that the risk induced by the loss of thrust can be assessed if none of the airports are reachable. The proposed method relies on planning space discretization and efficient risk propagation through the risk map. The approach can find the least risky landing site and corresponding forced landing trajectory for any configuration in the planning space. The method has been empirically evaluated in a realistic urban scenario. The results support its suitability for risk-aware planning of an emergency landing in the case of in-flight loss of thrust.

In this work-in-progress report, we present experimental results of lightweight learning-based leg-contact detection methods for a small hexapod walking robot with position feed- back only. The detection of the leg contact with the surface is addressed as anomaly detection using predicted and measured positions of the leg’s joints in the leg swing phase. A polynomial regressor and three-layer neural network are evaluated regarding the prediction error and computational requirements using realistic datasets collected with the real hexapod walking robot.

This paper concerns fault-tolerant power transmission line inspection planning as a generalization of the multiple traveling salesmen problem. The addressed inspection planning problem is formulated as a single-depot multiple-vehicle scenario, where the inspection vehicles are constrained by the battery budget limiting their inspection time. The inspection vehicle is assumed to be an autonomous multi-copter with a wide range of possible flight speeds influencing battery consumption. The inspection plan is represented by multiple routes for vehicles providing full coverage over inspection target power lines. On an inspection vehicle mission interruption, which might happen at any time during the execution of the inspection plan, the inspection is re-planned using the remaining vehicles and their remaining battery budgets. Robustness is introduced by choosing a suitable cost function for the initial plan that maximizes the time window for successful re-planning. It enables the remaining vehicles to successfully finish all the inspection targets using their respective remaining battery budgets. A combinatorial metaheuristic algorithm with various cost functions is used for planning and fast re-planning during the inspection.

Personal air transportation on short distances, so-called Urban Air Mobility (UAM), is a trend in modern aviation that raises new challenges as flying in urban areas at low altitudes induces an additional risk to people and properties on the ground. Risk-aware trajectory planning can mitigate the risk by detouring and flying over less populated and thus less risky areas. Existing risk-aware trajectory planning approaches are computationally demanding single-query methods that are impractical for online usage. Moreover, coordinated planning for multiple aircraft is prohibitively expensive. Therefore, we propose to reduce computational demands by determining low-risk areas called safe corridors and creating a roadmap of safe corridors based on multiple least risky trajectories. The created roadmap can be used in graph-based multi-agent planning methods for coordinated trajectory planning. The proposed method has been evaluated in a realistic urban scenario, suggesting a significant computational burden reduction and less risky trajectories than the current state-of-the-art methods.

Dubins tours represent a solution of the Dubins traveling salesman problem (DTSP) that is a variant of the optimization routing problem to determine a curvature-constrained shortest path to visit a set of locations such that the path is feasible for Dubins vehicle, which moves only forward and has a limited turning radius. The DTSP combines the NP-hard combinatorial optimization to determine the optimal sequence of visits to the locations, as in the regular TSP, with the continuous optimization of the heading angles at the locations, where the optimal heading values depend on the sequence of visits and vice versa. We address the computationally challenging DTSP by fast evaluation of the sequence of visits by the proposed windowing surrogate model (WiSM), which estimates the length of the optimal Dubins path connecting a sequence of locations in a Dubins tour. The estimation is sped up by a regression model trained using close to optimum solutions of small Dubins tours that are generalized for large-scale instances of the addressed DTSP utilizing the sliding-window technique and a cache for already computed results. The reported results support that the proposed WiSM enables fast convergence of a relatively simple evolutionary algorithm to high-quality solutions of the DTSP. We show that with an increasing number of locations, our algorithm scales significantly better than other state-of-the-art DTSP solvers.

This paper presents a novel approach to the multigoal trajectory planning for vehicles with curvature-constrained trajectories such as fixed-wing aircraft. In the existing formulation called the Dubins Traveling Salesman Problem (DTSP), the vehicle speed is assumed to be constant over the whole trajectory, and that does not allow adaptation of the turning radius of the trajectory between the target locations. It does not support optimization of the overall flight time of the multi-goal trajectory by exploiting higher speeds for longer turning radii. Therefore, we propose a novel problem formulation called the Variable-Speed Traveling Salesman Problem (VS-TSP) that employs time-efficient trajectories with variable speed based on a generalization of the Dubins vehicle model, allowing multiple turning radii and change of the forward speed of the vehicle. The VS-TSP allows the vehicle to slow down if high maneuverability is necessary and speed up if high-speed turns with a large radius are beneficial to the overall tour cost. Based on the evaluation results for Cessna 172 aircraft model, the proposed VNS-based algorithm with variable speed provides up to about 20 % faster trajectories than a solution of the DTSP with a single turning radius.

In this paper, we address the problem of finding cost-efficient three-dimensional paths that satisfy the maximum allowed curvature and the pitch angle of the vehicle. For any given initial and final configurations, the problem is decoupled into finding the horizontal and vertical parts of the path separately. Although the individual paths are modeled as two-dimensional Dubins curves using closed-form solutions, the final 3D path is constructed using the proposed local optimization to find a cost-efficient solution. Moreover, based on the decoupled approach, we provide a lower bound estimation of the optimal path that enables us to determine the quality of the found heuristic solution. The proposed solution has been evaluated using existing benchmark instances and compared with state-of-the-art approaches. Based on the reported results and lower bounds, the proposed approach provides paths close to the optimal solution while the computational requirements are in hundreds of microseconds. Besides, the proposed method provides paths with fewer turns than others, which make them easier to be followed by the vehicle's controller.

Motivated by observations of animal behavior, locomotion of multi-legged walking robots can be controlled by the central pattern generators (CPGs) that produce a repetitive motion pattern. A rhythmic pattern, a gait, is defined by phase relations between all leg joints. In a case of an external influence such as terrain irregularity, some actuator phase can shift and thus disrupt the phase relations between the actuators. The actuator phase relations can be maintained only by synchronizing to the sensors, which output can indicate the motion disruption. However, establishing correct sensory-motor phase relations requires not only the motor phase model but also a model of the sensory phase, which is generally unknown. Although both sensory and motor phases can be modeled by single CPG, the capabilities of such CPG-based controllers are limited because they are not flexible and robust. In this paper, we propose to model the phases of each sensor and motor by separate CPGs. The phase relations between the sensor and motor phases are established by radial basis function (RBF) neurons learned with proposed periodic Grossberg rule for which we present the convergence proof. Based on the reported evaluation results using high-fidelity simulation, the proposed locomotion controller demonstrates the desired plasticity, and it is capable of learning multiple gaits with robust synchronization to terrain changes using sensor inputs.

Multi-goal curvature-constrained planning such as the Dubins Traveling Salesman Problem (DTSP) combines NP-hard combinatorial routing with continuous optimization to determine the optimal vehicle heading angle for each target location. The problem can be addressed as combinatorial routing using a finite set of heading samples at target locations. In such a case, optimal heading samples can be determined for a sequence of targets in polynomial time, and the DTSP can be solved as searching for a sequence with the minimal cost. However, the examination of sequences can be computationally demanding for high numbers of heading samples and target locations. A fast rejection schema is proposed to quickly examine unfavorable sequences using lower bound estimation of Dubins tour cost based on windowing technique that evaluates short subtours of the sequences. Furthermore, the computation using small problem instances can benefit from reusing stored results and thus speed up the search. The reported results indicate that the computational burden is decreased about two orders of magnitude, and the proposed approach supports finding high-quality solutions of routing problems with Dubins vehicle.

Models of human behaviour, such as pedestrian flows, are beneficial for safe and efficient operation of mobile robots. We present a new methodology for benchmarking of pedestrian flow models based on the afforded safety of robot navigation in human-populated environments. While previous evaluations of pedestrian flow models focused on their predictive capabilities, we assess their ability to support safe path planning and scheduling. Using real-world datasets gathered continuously over several weeks, we benchmark state-of-the-art pedestrian flow models, including both time-averaged and time-sensitive models. In the evaluation, we use the learned models to plan robot trajectories and then observe the number of times when the robot gets too close to humans, using a predefined social distance threshold. The experiments show that while traditional evaluation criteria based on model fidelity differ only marginally, the introduced criteria vary significantly depending on the model used, providing a natural interpretation of the expected safety of the system. For the time-averaged flow models, the number of encounters increases linearly with the percentage operating time of the robot, as might be reasonably expected. By contrast, for the time-sensitive models, the number of encounters grows sublinearly with the percentage operating time, by planning to avoid congested areas and times.

This paper introduces the Close Enough Orienteering Problem (CEOP) for planning missions with multi-rotor aerial vehicles considering their maximal velocity and acceleration limits. The addressed problem stands to select the most rewarding target locations and sequence to visit them in the given limited travel budget. The reward is collected within a non-zero range from a particular target location that allows saving the travel cost, and thus collect more rewards. Hence, we are searching for the fastest trajectories to collect the most valuable rewards such that the motion constraints are not violated, and the travel budget is satisfied. We leverage on existing trajectory parametrization based on Bézier curves recently deployed in surveillance planning using unsupervised learning, and we propose to employ the learning in a solution of the introduced multi-vehicle CEOP. Feasibility of the proposed approach is supported by empirical evaluation and experimental deployment using multi-rotor vehicles.

Proprioceptive terrain sensing is essential for rough terrain traversal because it helps legged robots to negotiate individual steps by reacting to terrain irregularities. In this work, we propose to utilize inertial data in the detection of the contact between the leg and the terrain during the stride phase of the leg. We show that relatively cheap accelerometers can be utilized to reliably detect a foot-strike, and thus allow the robot to crawl irregular terrains. The continuous data processing is compared with the interrupt mode in which data are provided only around the foot-strike event. The interrupt mode exhibits significantly better performance, and it also supports generalization of the foot-strike event detector learned from data collected in slow locomotion to faster locomotion where the signals slightly change. The proposed solution is experimentally validated using a real hexapod walking robot for which the walking speed has been improved in comparison to the previous adaptive motion gait based on a force threshold-based position controller for the foot-strike detection.

The effectiveness of the robot locomotion can be measured using the cost of transport (CoT) which represents the amount of energy that is needed for traversing from one place to another. Terrains excerpt different mechanical properties when crawled by a multi-legged robot, and thus different values of the CoT. It is therefore desirable to estimate the CoT in advance and plan the robot motion accordingly. However, the CoT might not be known prior the robot deployment, e.g., in extraterrestrial missions; hence, a robot has to learn different terrains as it crawls through the environment incrementally. In this work, we focus on estimating the CoT from visual and geometrical data of the crawled terrain. A thorough analysis of different terrain descriptors within the context of incremental learning is presented to select the best performing approach. We report on the achieved results and experimental verification of the selected approaches with a real hexapod robot crawling over six different terrains.

Loss of thrust is a critical situation for human pilots of fixed-wing aircraft which force them to select a landing site in the nearby range and perform an emergency landing. The time for the landing site selection is limited by the actual altitude of the aircraft, and it may be fatal if the correct decision is not chosen fast enough. Therefore, we propose a novel RRT* -based planning algorithm for finding the safest emergency landing trajectory towards a given set of possible landing sites. Multiple landing sites are evaluated simultaneously during the flight even before any mechanical issue occurs, and the roadmap of possible landing trajectories is updated permanently. Thus, the proposed algorithm has the any-time property and provides the best emergency landing trajectory almost instantly.

In this paper, we propose a novel architecture for efficient detection of speeded-up robust features (SURF) for field-programmable gate array (FPGA). The main benefits of the proposed architecture are in real-time low-latency performance and scalability. The proposed solution provides a significant acceleration of salient points extraction that is fundamental image processing technique for vision-based methods including the simultaneous localization and mapping. Based on the presented practical results, the proposed architecture is capable of processing streaming image data at the rate of 140 Megapixels per second that roughly scales from the 640 × 480@420 fps up to 1920 × 1080@60 fps video streams on a low-end, low-cost FPGA solution (Cyclone V). Moreover, the proposed feature detection utilizes only about 20% of logic elements of the FPGA which supports further parallel processing of multiple inputs.

The self-organizing map (SOM) is an unsupervised learning technique providing a transformation of a high-dimensional input space into a lower dimensional output space. In this paper, we utilize the SOM for the traveling salesman problem (TSP) to develop a solution to autonomous data collection. Autonomous data collection requires gathering data from predeployed sensors by moving within a limited communication radius. We propose a new growing SOM that adapts the number of neurons during learning, which also allows our approach to apply in cases where some sensors can be ignored due to a lower priority. Based on a comparison with available combinatorial heuristic algorithms for relevant variants of the TSP, the proposed approach demonstrates improved results, while also being less computationally demanding. Moreover, the proposed learning procedure can be extended to cases where particular sensors have varying communication radii, and it can also be extended to multivehicle planning.

In this work, we are proposing a collision avoidance system for a hexapod crawling robot based on the detection of intercepting objects using the Lobula giant movement detector (LGMD) connected directly to the locomotion control unit based on the Central pattern generator (CPG). We have designed and experimentally verified the proposed approach that maps the output of the LGMD directly on the locomotion control parameters of the CPG. The results of the experimental verification of the system with real mobile hexapod crawling robot support the feasibility of the proposed approach in collision avoidance scenarios.

This paper concerns principles of unsupervised learning of self-organizing maps (SOMs) to address optimization routing problems called the Orienteering Problem (OP) and its multi-vehicle variant called the Team Orienteering Problem (TOP). The problems are similar to the traveling salesman problem in finding an optimal tour to visit all the given locations, but here, each location has specified reward that can be collected by the tour and the problem is to select the most valuable subset of the locations that can be visited within the travel budget. In existing SOM for the OP, the locations to be visited are duplicated to adapt the network to locations with higher rewards more frequently. The proposed novel SOM-based solution overcomes this necessity and based on the presented results it significantly reduces the computational burden of the adaptation procedure. Besides, the proposed approach improves the quality of solutions and makes SOM competitive to existing heuristics for the OP, but still behind computationally expensive metaheuristics for the TOP. On the other hand, the main benefit of the SOM-based approaches over the existing heuristics is in solving the generalized variant of the OP and TOP with neighborhoods. These variants of the problem formulation allow to better utilize the travel budget for instances where the reward associated with the location can be collected by visiting a particular neighborhood of the location and not exactly the location itself. This generalized problem formulation better models situations of the robotic data collection, e.g., using wireless communication or range sensors.

In this paper, we extent an existing self-organizing map (SOM)-based approach for the Dubins traveling salesman problem (DTSP) to solve its multi-vehicle variant generalized for visiting target regions called k-DTSP with Neighborhoods (k-DTSPN). The Dubins TSP is a variant of the combinatorial TSP for curvature-constrained vehicles. The problem is to determine a cost efficient path to visit a given set of continuous regions while the path allows to satisfy kinematic constraints of non-holonomic vehicles. The k-DTSPN is a generalization to determine k such paths, one for each vehicle. Although the k-DTSPN has been addressed by evolutionary methods, the proposed approach is able to provide solutions very quickly in units of seconds on conventional computationally resources which makes the proposed SOM-based approach suitable for on-line planning. The studied problem is motivated by surveillance task in which it is required to quickly provide information about the given set of target locations. Therefore, real computational requirements are crucial properties of the desired k-DTSPN solver. The proposed method meets this requirement and feasibility of the found solutions are demonstrated not only in computer simulations but also with a practical deployment on real aerial vehicles.

In this work, we concern the problem of motion planning for a hexapod walking robot crawling in a semi-structured environment where a precise foot-tip positioning is necessary. We propose pipelined approach utilizing an RGB-D camera to perceive and map the forthcoming terrain in 2.5 D which is then processed for available foot-tip positions. The robot motion control is based on sampling-based planning to determine the most suitable leg supporting configurations for the individual body positions in the created terrain map. The individual body positions are connected into a roadmap with taking into account a feasibility of the robot transition between the individual configurations. The resulting trajectory is then planned in the created roadmap using a standard A* planner. The proposed method has been experimentally evaluated in the on-line and onboard setup with a real hexapod crawling robot. The herein reported results support feasibility of the proposed approach for a precise motion planning of small hexapod crawling robot in a semi-structured environment.

In this paper, we address a generalization of the Orienteering Problem (OP) for curvature-constrained vehicles and to problems where it is allowed to collect a reward associated to each target location within a specified distance from the target. The addressed problem combines challenges of the combinatorial optimization of the OP (to select the most rewarding targets and find the optimal sequence to visit them) with the continuous optimization related to the determination of the waypoint locations and suitable headings at the waypoints for the considered Dubins vehicle such that the curvature-constrained path does not exceed the given travel budget and the sum of the collected rewards is maximized. The proposed generalization is called the Close Enough Dubins Orienteering Problem (CEDOP) and novel unsupervised learning approach is proposed to address computational requirements of this challenging planning problem. Based on the presented results, the proposed approach is feasible and provides a bit worse solution of CEDOP than the existing combinatorial approach but with significantly lower computational requirements.

This paper concerns a problem of the latency reduction in the vision-based mobile robot navigation, which is considered as the crucial system property to determine a control command based on visual data in practical deployments of mobile robots. The problem is addressed by a processor centric FPGA-based System-on-Chip design allowing power and computationally efficient on-line image processing. The proposed architecture is considered in an autonomous vision-based navigation with a teach-and-repeat algorithm based on detection and tracking of image salient points. The architecture has been evaluated and compared with a CPU-based solution on different platforms and the results indicate that the proposed FPGA-based implementation outperforms pure CPU solutions in the overall latency, speed, and power consumption.

In this paper, we consider existing asymptotically optimal inspection planning algorithm in coverage path planning with realistic visibility constraints of standard cameras. Although the existing approach is able to provide an optimal solution with omnidirectional sensing and limited sensing range, it is prohibitively computationally expensive for problems with only few objects to be covered and limited field of view. Based on the analysis of the utilized sampling-based strategy, we propose a heuristic approach to decrease computational requirements in problems with restricted viewing frustum, which is a more realistic model of a digital camera. In addition, we also consider a minimal distance and angle under which the object to be covered is captured by the forward looking camera to make a snapshot of the object with the required details.

In this paper, we consider road following to autonomously navigate a mobile robot through an environment while keeping the robot on the specified road. Contrary to existing approaches based on a forward looking camera, we consider the problem for a technically blind walking robot without any exteroceptive sensors. The only feedback considered is an estimation of tactile information that is determined from the robot servo drives. The proposed control law is based on an on-line classification of the previously learned terrains which is utilized to identify a situation when a robot starts to crawl off the desired road terrain. The controller steers the robot to keep its body and all its legs on the road while crawling forward with a constant velocity. The experimental results support feasibility of the proposed minimalistic approach and allows the robot to autonomously navigate in an outdoor environment and follow urban park pathways and avoid off-road parts.

We propose a self-organising map (SOM) algorithm as a solution to a new multi-goal path planning problem for active perception and data collection tasks. We optimise paths for a multi-robot team that aims to maximally observe a set of nodes in the environment. The selected nodes are observed by visiting associated viewpoint regions defined by a sensor model. The key problem characteristics are that the viewpoint regions are overlapping polygonal continuous regions, each node has an observation reward, and the robots are constrained by travel budgets. The SOM algorithm jointly selects and allocates nodes to the robots and finds favourable sequences of sensing locations. The algorithm has polynomial-bounded runtime independent of the number of robots. We demonstrate feasibility for the active perception task of observing a set of 3D objects. The viewpoint regions consider sensing ranges and self-occlusions, and the rewards are measured as discriminability in the ensemble of shape functions feature space. Simulations were performed using a 3D point cloud dataset from a real robot in a large outdoor environment. Our results show the proposed methods enable multi-robot planning for budgeted active perception tasks with continuous sets of candidate viewpoints and long planning horizons.

This paper concerns the self-localization problem of a hexapod walking robot operating in rough terrains. Given that legged robots exhibit higher terrain passability than wheeled or tracked platforms when operating in harsh environments, they constitute a challenge for the localization techniques because the camera motion between consecutive frames can be arbitrary due to the motion gait and terrain irregularities. In this paper, we present and evaluate an inertially assisted Stereo Parallel Tracking and Mapping (S-PTAM) method deployed on a hexapod crawling robot in a rough terrain. The considered deployment scenario is motivated by autonomous navigation in an unknown environment in an open loop fashion. The reported results and comparison with an existing RGB-D SLAM technique show the feasibility of the proposed approach and its suitability for navigation of crawlers in harsh environments.

In this paper, we address a problem of precise online localization of a hexapod walking robot operating in rough terrains. We consider an existing Simultaneous Localization and Mapping approach with a low cost structured light (RGB-D) sensor. We propose to combine this sensor and localization method with the developed adaptive motion gait that allows the robot to crawl various types of terrain, such as stairs, ramps, or small wooden blocks. Such an environment requires a full 6-DOF pose estimation to create a map of the robot surroundings and allows us to asses impact of the individual terrain types and influence of the SLAM method parametrization on the localization accuracy. The reported evaluation results indicate the relations between the terrain type, parametrization of the method and the localization accuracy.

In this paper, we address the Orienteering problem (OP) by the unsupervised learning of the self-organizing map (SOM). We propose to solve the OP with a new algorithm based on SOM for the Traveling salesman problem (TSP). Both problems are similar in finding a tour visiting the given locations; however, the OP stands to determine the most valuable tour that maximizes the rewards collected by visiting a subset of the locations while keeping the tour length under the specified travel budget. The proposed stochastic search algorithm is based on unsupervised learning of SOM and it constructs a feasible solution during each learning epoch. The reported results support feasibility of the proposed idea and show the performance is competitive with existing heuristics. Moreover, the key advantage of the proposed SOM-based approach is the ability to address the generalized OP with Neighborhoods, where rewards can be collected by traveling anywhere within the neighborhood of the locations. This problem generalization better fits data collection missions with wireless data transmission and it allows to save unnecessary travel costs to visit the given locations.

This paper introduces an extension of the unsupervised learning method to solve data collection planning problems where particular sensor measurements can be spatially correlated. The problem is motivated by monitoring tasks formulated as the Prize-Collecting Traveling Salesman Problem with Neighborhoods (PC-TSPN). A solution of the PC-TSPN consists of a selection of important sensors, determination of the locations to read data from these sensors, and finding the shortest path to visit the locations. The solution cost is defined as a sum of the travel cost and penalty characterizing additional cost associated to sensors from which data are not retrieved. The penalty represents importance of particular sensor measurements to the quality of the model and existing solutions assume the penalties are constant values. However, for spatially close sensor locations, data from one sensor may contain also information about nearby locations and thus, its penalty depends on locations selected for data collection. The proposed generalization of the PC-TSPN solver allows to consider spatial correlations of sensor measurements and the proposed approach provides better solutions than the previous algorithm with fixed penalties.

In this paper, we address the problem of optimal path planning to visit a set of regions by Dubins vehicle, which is also known as the Dubins Traveling Salesman Problem with Neighborhoods (DTSPN). This problem can be tackled by a transformation to other variants of the TSP or evolutionary algorithms. We address the DTSPN as a problem to find Dubins path to visit a given sequence of regions and propose a simple iterative optimization procedure to find Dubins path visiting the regions. The proposed approach allows to efficiently solve the DTSPN and based on the presented comparison with existing approaches, the proposed algorithm provides solutions of competitive quality to the evolutionary techniques while it is significantly less computationally demanding.

This paper presents our early results on multi-goal trajectory planning with motion primitives for a hexapod walking robot. We propose to use an on-line unsupervised learning method to simultaneously find a solution of the underlying traveling salesman problem together with particular trajectories between the goals. Using this technique, we avoid pre-computation of all possible trajectories between the goals for a graph based heuristic solvers for the traveling salesman problem. The proposed approach utilizes principles of self-organizing map to steer the randomized sampling of configuration space in promising areas regarding the multi-goal trajectory. The presented results indicate the proposed steering mechanism provides a feasible multi-goal trajectory in a less number of samples than an approach based on a priori known sequence of the goals visits.

In this paper, we propose a framework for solving variants of the multi-goal path planning problem with applications to autonomous data collection. Autonomous data collection requires optimizing the trajectory of a mobile vehicle to collect data from a number of stationary sensors in a known configuration. The proposed approach utilizes the self-organizing map (SOM) architecture to provide a unified solution to multi-goal path planning problems. Our approach applies to cases where the vehicle must move within a radius of a sensor to collect data and also where some sensors can be ignored due to a lower priority. We compare our proposed approach to state-of-the-art approximate solutions to variants of the Traveling Salesman Problem (TSP) for random deployments and in an underwater monitoring application domain. Our results demonstrate that the SOM approach outperforms combinatorial heuristic algorithms and also provides a unified approach for solving variants of the multi-goal path planning problem.

In this paper, we present a small, light-weight, low-cost, fast and reliable system designed to satisfy requirements of relative localization within a swarm of micro aerial vehicles. The core of the proposed solution is based on off-the-shelf components consisting of the Caspa camera module and Gumstix Overo board accompanied by a developed efficient image processing method for detecting black and white circular patterns. Although the idea of the roundel recognition is simple, the developed system exhibits reliable and fast estimation of the relative position of the pattern up to 30 fps using the full resolution of the Caspa camera. Thus, the system is suited to meet requirements for a vision based stabilization of the robotic swarm. The intent of this paper is to present the developed system as an enabling technology for various robotic tasks.

In this paper, we present a supporting structure for speeding up visibility queries needed for a 3D multi-goal path planning arising from a robotic coverage problem where goals are sensing locations from which an object of interest can be covered. Although such coverage problems can be addressed by a decomposed approach where sensing locations are determined prior finding the sequence of their visits, the proposed approach is motivated by a solution of the problem in which sensing locations are simultaneously determined together with evaluation of the path connecting them in order to provide a cost effective inspection path. The proposed structure divides the space into elements that support determination of suitable sensing locations to cover the objects during solution of the multi-goal path planning.

In this paper, a cooperative driver model for a multi-agent traffic simulation is proposed. The model combines maneuver-based trajectory planning of the vehicles with a cooperative conflict resolving. The proposed model is able to provide a safe drive in complex traffic situations at the highest possible speed. The idea of the model and its feasibility have been verified in complex scenarios such as line change under heavy traffic, highway entering or highway crossing. Moreover, the developed cooperative driver model is being integrated with a human operated driving simulator that enables verification of the proposed model in mixed scenarios enriching the simulation for a human driver with highly cooperative background traffic; thus, providing a platform for further studies on benefits of assistive technologies. The paper provides description of the proposed model and its early evaluation on the selected scenarios in a multi-agent traffic simulation.

In this paper, the multi-robot motion coordination planning problem is addressed. Although a centralized prioritized planning strategy can be used to solve the problem, we rather consider a decentralized variant, which is a more suitable for a robotic system of cooperating unmanned aerial vehicles (UAVs) due to communication limitations, privacy concerns, and a better exploitation of computational resources distributed among the individual robots. However, the existing decentralized prioritized planning algorithm contains synchronization points that all the agents must be able to pass synchronously, which is impractical and inefficient for a real-world deployment of the robotic systems. Therefore, we introduce a new asynchronous decentralized prioritized planning algorithm and show that the method can converge faster than both the synchronous decentralized and centralized algorithms. Further, we demonstrate the applicability of the proposed method as a coordination mechanism within a complex mission planning for a real robotic system consisting of several autonomous UAVs.

This paper presents a multi-goal path planning framework based on a self-organizing map algorithm and a model of the navigation describing evolution of the localization error. The framework combines finding a sequence of goals' visits with a goal-to-goal path planning considering localization uncertainty. The approach is able to deal with local properties of the environment such as expected visible landmarks usable for the navigation. The local properties affect the performance of the navigation, and therefore, the framework can take the full advantage of the local information together with the global sequence of the goals' visits to find a path improving the autonomous navigation. Experimental results in real outdoor and indoor environments indicate that the framework provides paths that effectively decreases the localization uncertainty; thus, increases the reliability of the autonomous goals' visits.

In this paper, we discuss the problem of goal assignment in the multi-robot exploration task. The presented work is focused on the underlying optimal assignment problem of the multi-robot task allocation that is addressed by three state-of-the art approaches. In addition, we propose a novel exploration strategy considering allocation of all current goals (not only immediate goal) for each robot, which leads to the multiple traveling salesman problem formulation. Although the problem is strongly NP-hard, we show its approximate solution is computationally feasible and its overall requirements are competitive to the previous approaches. The proposed approach and three well-known approaches are compared in series of problems considering various numbers of robots and sensor ranges. Based on the evaluation of the results the proposed exploration strategy provides shorter exploration times than the former approaches.

Several navigation tasks utilizing a low-cost Micro Aerial Vehicle (MAV) platform AR-drone are presented in this paper to show how it can be used in an experimental verification of scientific theories and developed methodologies. An important part of this paper is an attached video showing a set of such experiments. The presented methods rely on visual navigation and localization using on-board cameras of the AR-drone employed in the control feedback. The aim of this paper is to demonstrate flight performance of this platform in real world scenarios of mobile robotics.

In this paper, we present a novel path planning algorithm based on properties that reaction-diffusion (RD) models exhibit by the underlying non-linear dynamics of the considered system. In particular herein considered a two-variable RD model provides advantages of natural parallelism, noise resistance, and especially the non-annihilating feature that traveling fronts separating two stable states exhibit upon a collision. Based on this, we developed a path planning algorithm that provides paths with lengths competitive to standard path planning approaches. Moreover, the results presented indicates the paths are smoother and also within a safe distance from obstacles; thus, the found paths combine advantages of two fundamental approaches, namely the DT algorithm and Voronoi diagram.

Performance of exploration strategies strongly depends on the process of determination of a next robot goal. Current approaches define different utility functions how to evaluate and select possible next goal candidates. One of the mostly used evaluation criteria is the distance cost that prefers candidates close to the current robot position. If this is the only criterion, simply the nearest candidate is chosen as the next goal. Although this criterion is simple to implement and gives feasible results there are situations where the criterion leads to wrong decisions. This paper presents the distance cost that reflects traveling through all goal candidates. The cost is determined as a solution of the Traveling Salesman Problem using the Chained Lin-Kernighan heuristic. The cost can be used as a stand-alone criterion as well as it can be integrated into complex decision systems. Experimental results for open-space and office-like experiments show that the proposed approach outperforms the standard one in the length of the traversed trajectory during the exploration while the computational burden is not significantly increased.

In this paper, a new self-organizing map (SOM) based adaptation procedure is proposed to address the multiple watchman route problem with the restricted visibility range in the polygonal domain W. A watchman route is represented by a ring of connected neuron weights that evolves in W, while obstacles are considered by approximation of the shortest path. The adaptation procedure considers a coverage of W by the ring in order to attract nodes toward uncovered parts of W. The proposed procedure is experimentally verified in a set of environments and several visibility ranges. Performance of the procedure is compared with the decoupled approach based on solutions of the art gallery problem and the consecutive traveling salesman problem. The experimental results show the suitability of the proposed procedure based on relatively simple supporting geometrical structures, enabling application of the SOM principles to watchman route problems in W.